What if the Chicxulub meteor had missed the Earth?

In a world where an asteroid whizzed past Earth instead of crashing down with the force of 100 million tons of TNT, life could have progressed much differently. Sixty-five million years ago, some of the animals and plants that are common today were just getting started. These include placental mammals and angiosperms, or flowering plants. Insects that rely on flowers, such as bees, were also relatively new. Many of these life forms thrived after the K-T event, and without the mass extinction to clear the way, they may not have found ecological niches to fill. In this scenario, today's world might be full of reptiles and short on mammals -- including people.

But even if the asteroid hadn't hit, dinosaurs and other Cretaceous life forms might have become extinct anyway. Some dinosaur species had started to dwindle long before the asteroid's impact. This has led most researchers to conclude that the asteroid was just one aspect of a complex event. Other global catastrophes, like massive volcanic eruptions in what is now India, most likely played a role. Also, the Earth's changing landscape as the supercontinent Pangaea broke up into today's continents probably had something to do with it, too.

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Then there's another argument -- that the Chicxulub asteroid hit the Earth too early to have caused the extinction. Researchers Gerta Keller and Markus Harting both conclude that the impact took place 300,000 years before the end of the Cretaceous period. Keller, of Princeton University, theorizes that the Chicxulub impact was one of at least three massive collisions [source: Schultz]. Harting, of the University of Utrecht, argues that the iridium layer didn't come from the Chicxulub asteroid but from another event, such as a series of meteors burning up in the atmosphere. He bases this theory on spheroid particles ejected during the impact. Most of these are in an older layer of the Earth than the K-T iridium layer [source: Cairns]. According to both of these points of view, the absence of the Chicxulub asteroid strike may not have had a big effect on the K-T extinction.

It's hard to come to a definitive conclusion about what the world would look like today without the Chicxulub impact. But the question of whether people and dinosaurs could have coexisted is a captivating one. The idea is present in everything from the Congo legend of Mokele-Mbembe to "King Kong" and an episode of the BBC series "Horizon" called "My Pet Dinosaur." Then, of course, there's the prevailing scientific theory about the origin of birds -- that they are, in essence, living dinosaurs. You can read more about all the competing theories on the next page.

Dinosaurs and Global Cooling

Earth was a warm planet for most of the time that dinosaurs lived. After the end of the Cretaceous period, the world got a lot colder and experienced several ice ages. Whether dinosaurs could have survived such a change in climate is debatable.